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Multiple Select Problems (or Checkbox Multiple Choice or Select All That Apply)

This code snippet shows the essential PG code to include multiple select question (or checkbox multiple choice or select all that apply) in a problem. A multiple choice question has only one correct answer, whereas a checkbox multiple choice question may require several items to be selected at the same time to be correct.

Note that in this example we use old-style checkbox multiple choice answer objects. The new-style MathObjects do not yet have a checkbox multiple choice answer object.

Problem Techniques Index

PG problem file Explanation



Initialization: We must load and

$mc = new_checkbox_multiple_choice();
$mc -> qa (
"Select all expressions that are equivalent to  
\( e^{x^2 + 1/x} \).  There may be more than
one correct answer.", 
"\( e^{x^2} e^{1/x} \)$BR",
"\( e^{x^2} e^{x^{-1}} \)$BR",                
"\( e^{ (x^3+1) / x } \)$BR",
$mc -> extra(
"\( \displaystyle \frac{ e^{x^2} }{ e^x } \)$BR",
"\( e^{x^2} + e^{1/x} \)$BR",
$mc -> makeLast("None of the above");

Setup: Create a new checkbox multiple choice object named $mc with $mc->new_checkbox_multiple_choice();.

Use the question and answer method qa( ) to store the question string and correct answer strings in $mc. For example, $mc->qa("question","correct answer 1","correct answer 2");. Note that unlike match lists and select lists, you cannot call the qa( ) method again. If you include math symbols you should switch to LaTeX mode \( \), and use \displaystyle with extra spacing $BR after each entry, if necessary. For example, $mc->qa("question", "\( x^2 \) $BR", "\( \displaystyle \frac{x^2}{4-x} \) $BR" );

Incorrect answers are specified as a list of string arguments to the extra( ) method.

The arguments of the makeLast( ) method will appear at the end of the list and will not be shuffled, unlike the arguments of extra( ), which are shuffled. The arguments to makeLast( ) can either be a new extra answers or only the correct answer. For example, if the only correct answer is "None of the above", use

$mc->qa("question","None of the above");
$mc->extra("very wrong","distractor","red herring");
$mc->makeLast("None of the above");

To make answers appear in a certain order (e.g., Yes followed by No and Maybe), use $mc->qa("question","Yes"); $mc->makeLast("Yes","No","Maybe"); and do not use extra( ) at all. In this case, to randomize the question and answer, where the answer to question 1 is Yes and the answer to question 2 is No, use

@quest = ("question 1","question 2"); 
@ans = ("Yes","No"); 
$pick = random(0,1,1);


\{ $mc -> print_q() \}
\{ $mc -> print_a() \}


Main Text: Print the question and answers. Print the question text using $mc->print_q() and the list of all answers using $mc->print_a().


$showPartialCorrectAnswers = 0;

ANS( checkbox_cmp( $mc->correct_ans() ) );


Answer Evaluation: We use the standard problem grader, an all-or-nothing grader that gives no partial credit, and set $showPartialCorrectAnswers = 0; to withhold credit and hide the correct answers until the student answers everything correctly. Otherwise, the student can use a guess-and-check method to find the correct answers by the partial credit and feedback received. Use the checkbox_cmp answer checker.

See the linked forum discussion thread for a technique to give partial credit on such questions.

Problem Techniques Index